This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Traditional risk factors (e.g., lipoproteins, inflammation, oxidative stress) explain only half the risk of atherosclerotic disease. We believe that the response of the arterial wall to circulating risk factors accounts for a significant proportion of the remaining risk. Arterial wall is where the vascular pathological changes occur, and it determines endogenous susceptibility to vascular diseases. Furthermore, mobilization of circulating endothelial progenitor cells (CEPCs) in response to vascular injury plays a major role in the initiation and progression of atherosclerosis. In this project, we will first test the hypothesis that genetic variation is the major determinant of endothelial responses to atherogenic stimuli and consequently is largely responsible for variation in susceptibility to atherosclerosis. Using arterial biopsies, we will collect macrovascular endothelial cells (ECs) from 405 pedigreed baboons, and will subject these cells to in vitro pro-atherogenic challenges. We will measure markers of endothelial dysfunction including mRNA and protein levels of eNOS, VCAM-1, ICAM-1, E-Selectin, vWF and MCP-1, and percentage of apoptosis before and after endothelial cells are activated. Second, we will test the hypotheses that the basal number of circulating CEPCs is regulated genetically, and that the number of mobilized CEPCs in response to vascular injury is also genetically controlled. We will collect blood prior to and after in vivo vascular injury by femoral artery ligation from 450 baboons on basal diet and 80 after a 7-wk challenge and we will quantify CEPC number in the blood by flow cytometry before and 72 hr post injury to evaluate the induction of mobilized progenitor cells. The results will be subjected to genome wide scans to identify chromosomal regions that harbor genes affecting endothelial function, or number of CEPCs. Third, we will test the hypothesis that EC functional properties and CEPC numbers predict susceptibility to atherosclerotic lesions in a study of 111 baboons fed atherogenic diet for 2 yr prior to necropsy and assessment of lesions. Fourth, we will test the hypothesis that an atherogenic diet hampers CEPC differentiation capacity by conducting functional assays on cultured CEPCs from 120 baboons before and during a 2-yr dietary challenge, and before and after femoral artery biopsy. The ultimate goal is to identify genes that regulate functional responses to atherogenic risk factors in mature endothelial cells lining arterial wall and in progenitor endothelial cells circulating in the blood. Our project will establish a nonhuman primate model that can be used for pharmacological and interventional investigations of vascular diseases with direct assessment of arterial wall endothelial function.